fix splitter filters being lost when rotating in place and add test

src/lib/sim/BuildingSystem.cpp

@@ -1719,29 +1719,25 @@ void BuildingSystem::rotateInPlace(BuildingId id, Rotation newRotation)
         // the new port set (REQ-MAT-INPUT-INTAKE).
         b.incomingItems.assign(b.inputPorts.size(), {});
 
-        // Re-register with BeltSystem (items on tile are discarded).
+        // Re-register with BeltSystem (items on tile are discarded). A splitter's
-        if (b.type == BuildingType::Belt)
+        // filters live in BeltSystem and would be lost by removeTile, so capture
+        // them first and hand them back to reregisterBeltTile (REQ-BLD-SPLITTER).
+        if (isBeltSubsystemType(b.type))
         {
+            std::vector<ItemType> splitterFilterA;
+            std::vector<ItemType> splitterFilterB;
+            if (b.type == BuildingType::Splitter)
+            {
+                if (const std::optional<BeltSystem::SplitterInfo> info =
+                        m_belts.getSplitterInfo(b.anchor))
+                {
+                    splitterFilterA = info->filterA;
+                    splitterFilterB = info->filterB;
+                }
+            }
+
             m_belts.removeTile(b.anchor);
-            m_belts.placeBelt(b.anchor, newRotation);
+            reregisterBeltTile(b, splitterFilterA, splitterFilterB);
-        }
-        else if (b.type == BuildingType::Splitter)
-        {
-            m_belts.removeTile(b.anchor);
-            assert(mask.outputPorts.size() >= 2);
-            m_belts.placeSplitter(b.anchor,
-                                  mask.outputPorts[0].direction,
-                                  mask.outputPorts[1].direction);
-        }
-        else if (b.type == BuildingType::TunnelEntry)
-        {
-            m_belts.removeTile(b.anchor);
-            m_belts.placeTunnelEntry(b.anchor, newRotation, m_config.world.tunnelMaxDistance_tiles);
-        }
-        else if (b.type == BuildingType::TunnelExit)
-        {
-            m_belts.removeTile(b.anchor);
-            m_belts.placeTunnelExit(b.anchor, newRotation);
         }
 
         return;

src/test/BuildingTest.cpp

@@ -1427,6 +1427,36 @@ TEST_CASE("BuildingSystem: rotateInPlace re-registers a belt tile with BeltSyste
     REQUIRE(belts.tryPutItem(QPoint(0, 0), makeItem("iron_ore")));
 }
 
+TEST_CASE("BuildingSystem: rotateInPlace preserves the output filters of a splitter "
+          "(REQ-BLD-SPLITTER)", "[building][rotate-in-place]")
+{
+    PlacementFixture f;
+
+    const QPoint tile(5, 5);
+    const BuildingId id = f.bs.place(BuildingType::Splitter, tile, Rotation::East, 0).value();
+
+    // Run until construction completes, so the splitter is registered with BeltSystem.
+    Tick tick = 0;
+    while (f.bs.getAllBuildings().empty() && tick < 100000)
+    {
+        runTicks(f.bs, f.belts, 1, tick);
+    }
+    REQUIRE(f.bs.getAllBuildings().size() == 1);
+
+    const std::vector<ItemType> filterA{ ItemType{"iron_ore"} };
+    const std::vector<ItemType> filterB{ ItemType{"copper_ore"} };
+    f.belts.setSplitterFilters(tile, filterA, filterB);
+
+    f.bs.rotateInPlace(id, Rotation::North);
+
+    // The tile is re-registered with BeltSystem carrying the filters it had before
+    // the rotation — rotating must not reset a configured splitter to "accept all".
+    const std::optional<BeltSystem::SplitterInfo> info = f.belts.getSplitterInfo(tile);
+    REQUIRE(info.has_value());
+    REQUIRE(info->filterA == filterA);
+    REQUIRE(info->filterB == filterB);
+}
+
 TEST_CASE("BuildingSystem: splitter filters configured on a construction site carry over "
           "to the built splitter (REQ-BLD-SITE-CONFIG)", "[building]")
 {